All of the cell sites I've ever built have battery backup and emergency generators. The batteries are mostly for power filtration and the few minutes between power outage and generators achieving full power. The generators are to keep the air conditioning working, tower lights and to charge the batteries. If its a huge outage, like from a hurricane, the sites will start dropping off after 3 days on average unless the generators can be re-fueled.
Randy Rosetta KDØKWX TLCA #19351 69 FJ40 "Meanie" & 1970 Boss 302 Mustang